Merino made 45 appearances for Real Sociedad in 2023/24, scoring eight goals and assisting a further four.
As mentioned, he previously played in the Premier League with Newcastle United for a season, making 25 appearances in 2017/18 before moving on to La Liga.
The midfielder was a regular for Spain at Euro 2024, appearing in every game albeit largely off the bench. He had a pivotal impact in the quarter-final against Germany, scoring the winning goal.